4.3.3 Plant disease

Question 1

How do aphids cause damage to plants?

Answer 1

They use their sharp mouthparts to extract sap from the plant phloem, weakening the plant. They are also vectors who can transfer pathogens from diseased plants to healthy plants.

Question 2

How can we reduce the number of aphids?

Answer 2

• Chemical pesticides
• Biological pest control - Using ladybirds

Question 3

Why do plants need a good supply of nitrate ions?

Answer 3

Nitrate ions are required to convert sugars into proteins which are required for the plant to grow. As a result, the growth of the plant will be stunted if there is an adequate supply of nitrates.

Question 4

Why do plants need a good supply of magnesium ions?

Answer 4

Magnesium ions are required to synthesise chlorophyll, which absorbs light energy during photosynthesis. As a result, the leaves cannot photosynthesise properly and they turn yellow (chlorosis)

Question 5

What are the symptoms of disease in plants?

Answer 5

• Stunted growth (lack of nitrate ions)
• Spotted leaves (e.g. rose black spot fungus)
• Decay/rotting
• Growths
• Malformation of stems/leaves
• Discolouration
• Presence of pests

Question 6

What are three ways in which plant disease can be identified?

Answer 6

• Reference to a gardening website or manual
• Laboratory testing
• Monoclonal antibody test kits

Question 7

Give examples of physical defence responses used by plants

Answer 7

• Cellulose cell walls
• Tough, waxy cuticle on leaves
• Outside layer on stems/bark on trees
• leaf fall

Question 8

Give examples of chemical defence responses used by plants

Answer 8

• Antibacterial chemicals
• Poisons

Question 9

Give examples of mechanical defence responses used by plants

Answer 9

• Thorns and hairs to deter animals
• Leaves that droop/curl on contact
• Mimicry to trick animals